The prior art is replete with various aircraft flight control instruments and displays. Such flight control displays, which may be of the panel mounted variety or of the head up display (HUD) variety, are commonly found in commercial, military, and civilian aircraft. One well known display instrument is an attitude direction indicator (ADI). An ADI typically indicates a reference point or line, e.g., a representative horizon line, relative to the position of the host aircraft. The aircraft may be represented by a fixed element of the ADI display; most ADIs depict the aircraft wings as one or more horizontal marks that are centered with respect to the display screen. The horizon line rendered on the ADI display may move up and down in response to changes in the pitch of the aircraft. Similarly, the horizon line may rotate in response to changes in the roll of the aircraft.
Many conventional ADIs include a blue colored portion above the horizon line (representing the sky) and a brown or tan colored portion below the horizon line (representing the Earth). This color scheme is employed to enable pilots to determine the attitude of the aircraft at any given moment. The color scheme is particularly helpful in situations where the pilot may be temporarily distracted or in situations where visibility is impaired. While an ADI having such a color scheme may be suitable in many situations, a pilot may have difficulty detecting small changes in tilt and roll based on slight movement of the horizon line and/or slight movement of the blue and brown colored segments.
In addition to the horizon line indication, conventional ADIs may also be configured to convey flight guidance information to the pilot. Such guidance information may be related to an approach target, e.g., a runway, or any reference point. The ADI may respond to an electronic landing system signal to display information that enables the pilot to fly the aircraft in an appropriate manner. Typically, the target information is rendered in the form of one or more alphanumeric "overlay" images that convey quantitative flight information to the pilot in conjunction with the other images discussed above. Unfortunately, such overlay images may be difficult to read and interpret under certain flight conditions, particularly when the pilot cannot concentrate his or her attention on the ADI.
ADIs and other related instrumentation may display alphanumeric or graphical information related to the direction of the aircraft relative to a specific reference point such as the horizon. However, the manner in which such information is typically displayed requires the pilot to scan the instrumentation panel (or HUD field), locate the displayed information, and interpret the information. Depending upon the current flight conditions, it may be difficult for a pilot to quickly and easily locate and digest such information. Consequently, the reaction time associated with adjusting the direction of the aircraft toward the reference point may be undesirably long.
Accordingly, it would be desirable to have an ADI having features that address the above shortcomings of the prior art.